FileReader循环上传图片到七牛

function uploadImg(event) {
    var length = 0;

    var e=window.event||event;
    var that = e.target;

    var serial = $(that).attr('data-serial');
    var id = $('meta[name=order_id]').attr('content');
    var order_status = $('meta[name=order_status]').attr('content');

    $(that).attr('value','');
    // 获取当前选中的文件
    var length = e.target.files.length;

    console.log(length);

    // 判断文件的数量
    if(length > 30){
        alert("单次文件上传数量不能大于30张！");
        return;
    }

    // 判断文件的尺寸
    for (var i=0 ;i< length; i++) {
        var file = e.target.files[i];
        if(file.size > 10*1024 * 1024){
            alert("文件尺寸不能大于10M");
            return;
        }
    }
    //需要上传的图片内容 base64格式
    var imgStr = '';
    //七牛云平台 配置的域名
    // var urlHeader = "http://qiniu.yunyidai.net/";
    //获取七牛的token
    var qiniuParams = {
        url: '/admin/common/qiniu/upload/token',
        type: 'get',
        data: {},
        header: {},
        async: false,
        callback: function(res){
            qiniutoken = res.data;
        }
    };
    ajaxRequest(qiniuParams);
    // 追加到from对象
    for (var i=0 ;i< length; i++) {
        var file = e.target.files[i];
        var prifix = file.name.split('.')[1];
        //文件后缀
        // console.log(file);
        //七牛云图片base64格式上传地址
        // document.write(uploadUrl);
        var reader = new FileReader();
        reader.readAsDataURL(file);
        reader.onload = function(ev) {
            var uploadUrl = "https://upload.qiniup.com/putb64/-1/key/" + window.btoa("customer_"+ parseInt(Math.random()*9999999) + new Date().getTime()+"_"+parseInt(Math.random()*9999999) + '.' + prifix);

            //获取到base64格式的图片
            var imgStr = ev.target.result.split(',')[1];
            // console.log(imgStr)
            $.ajax({
                headers: {
                    'Authorization' : "UpToken " + qiniutoken
                },
                url: uploadUrl,
                type: 'POST',
                data: imgStr,
                async: false,
                success: function (res) {
                    var file_path = qiniuhost + '/' + res.key;
                    $.ajax({
                        headers: {
                            'X-CSRF-TOKEN': csrf_token
                        },
                        url: '/admin/customer/document/upload',
                        type: 'post',
                        async: false,
                        data:{
                            id: id,
                            serial: serial,
                            order_status: order_status,
                            file_path: file_path,
                        },
                        success: function (res){
                            var html = '';
                            html += '<div style="margin-left: 5px;" class="customer_detail_file_size serialid_'+serial + '">';
                            html += '<div><img src="'+ file_path +'" alt=""></div>';
                            html += '<div><span data-file_path="'+ file_path +'" class="customer_detail_file_del">删除</span></div>';
                            html += '</div>';

                            $('.serialid_'+serial).last().after(html);

                        },
                        error: function (res) {
                            parent.layer.msg('网络异常', {time: 1000});
                        }
                    });
                }
            });
        }
        // reader.abort();
        sleep(100);
    }
}